Try to finish the upgrade by opening a terminal and typing or pasting this:

sudo dpkg --configure -a

You can also try
sudo apt-get -f install

If this does not fix it then you can try the recovery mode from grub. It
should allow you to finish the upgrade.

Let us know if this does not fix it and what error messages you are seeing.

how do you recover from grub?

It all depends on the version that you are running. Newer versions have a
grub entry that say (recovery mode). It is usually the third or so entry.
Just cursor down and press enter. Use the latest kernel with recovery mode
after it.

This is how it works:
unixlab.blogspot.com/.../...ntu-recovery-mode.html

The original poster will want the third entry Repair broken packages.

Boot into the 10.04 installation and then open Terminal to run the
following commands ...

sudo dpkg configure -a

sudo apt-get upgrade fix-broken

That should sort it for you :-)

FWIW - upgrades can always be flaky anyway so if this still doesn't
sort it you may be looking at a clean install of 10.10 instead. Not as
difficult as that may seem ( apart from the saving data etc ). First
of all boot into Windows and delete all non-windows partitions to
leave a single empty partition then use a 10.10 Live CD to do the
install and when asked where it has to go you select the empty
partition and let it do a clean install. This will also sort out the
dual-boot menu too.

Purists may feel booting with a Live CD and using GParted to delete
the partitions not required is a better way of course, but letting
Windows do the deleting is possibly less traumatic for poor Windows

Download and burn the Puppy LuPu 525 Live CD, upon starting it should find your
Ubuntu installation and offer to repair if it sees an "unclean hard drive"
shutdown situation. Did you try to run Ubuntu 10.10 from Live CD to select
repair of Ubuntu? From Ubuntu Live CD, go to System>Administration>Disk
Utility...you'll see Smart and Check file system...Report back if you need more
help.
Don't worry for the Windows' side, since your Windows' Install CD can repair it
to start over with a clean Ubuntu install. Puppy or Ubuntu Live CDs can mount
and copy files from the hard drive to an external USB mounted hard drive, too.